This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-288428, filed Sep. 22, 2000, the entire content of which is incorporated herein by reference.
The present invention relates to a silver halide emulsion having a high sensitivity and excellent manufacturing suitability (stability of a dissolved coating liquid over time), and a silver halide photographic light-sensitive material using the same.
Recently, in order to match with widely available digital cameras, a silver halide emulsion for photography is desired to have a higher sensitivity and ensure excellent image quality. In particular, a light-sensitive material for color photography having a high sensitivity and ensuring high image quality, capable of being used even in inexpensive cameras which tend to have an insufficient amount of strobe light, such as a lens-fitted film, is strongly desired. As a technique for enhancing the sensitivity of the silver halide emulsion and ensuring the image quality, tabular grains can be used. Known advantages of the tabular grains are, e.g., improvements of the sensitivity, including improvements of the spectral sensitization efficiency obtained by sensitizing dyes, improvements of the sensitivity/graininess ratio, improvements of the sharpness obtained by the specific optical properties of the tabular grains, and improvements of the covering power. In general, the higher the aspect ratio of the tabular grains, the more the sensitivity/graininess ratio is improved, provided that the volumes of the grains are the same.
However, no description relating to an emulsion recited in the claims of the present application is found in patent specifications which disclose the aforementioned tabular grains.
It is an object of the present invention to provide a silver halide photographic emulsion having a high sensitivity and excellent manufacturing suitability (stability of a dissolved coating liquid over time), and a silver halide photographic light-sensitive material using the same.
The inventor has sought to increase the sensitivity of a halide photographic emulsion, using such means as making the tabular grain thinner, introducing high density dislocation lines at a fringe portion of the grains, and chemically sensitizing the emulsion by monodispersing the distribution of equivalent circle diameters. On the other hand, the inventor has found that non-uniformity (sensitivity lowering) in the photographic performance of the silver halide emulsion occurs, as the grains become thinner. It has also been found that the longer the coating liquid is left in a dissolved state over time just before the coating, the greater the degree of sensitivity decrease is; the coating liquid being prepared by mixing the silver halide emulsion, an emulsified product including a coupler, and other chemicals. In the actual manufacture of a silver. halide photographic light-sensitive material, the period of time the coating liquid is kept in a dissolved state varies, due to unexpected causes. In such a case, a silver halide emulsion having a non-uniform sensitivity is unpreferable. Consequently, the inventor has made efforts to eliminate the non-uniformity and found the following. That is, when viewed from a direction perpendicular to a (111) main plane, the coating liquid which contains an emulsion having a large proportion of hexagonal or triangular tabular grains whose edge and/or corner are partly hollowed toward inside thereof, has a higher stability over time when it is dissolved (the sensitivity reduction due to time lapse is small). When the grains of the emulsion were directly observed by a transmission electron photomicrograph, it was observed that the edges and/or corners of the tabular grains were slightly rounded during the period the coating liquid kept in a dissolved state over time. However, the percentage of tabular grains with partly hollowed edges and/or corners after the coating did not significantly vary to that before the coating. It is not certain why the coating liquid which contains an emulsion having a large proportion of tabular grains whose edges and/or corners are partly hollowed, as a result, had a sensitivity which is less reduced during the period the coating liquid remained in a dissolved state. However, it appears that such a small change as to be virtually undetectable even by transmission electron photomicrograph, occurs. In an emulsion having a large proportion of tabular grains with partly hollowed edges and/or corners, such a change already occurred while preparing the emulsion. Afterwards, during the time the coating liquid remained in a dissolved state, such a change that causes a large reduction of the sensitivity may not occur. As described above, the inventor has achieved, for the first time, by the following solving means, the object of coping with both the sensitivity of the silver halide photographic emulsion and the manufacturing suitability (stability of a dissolved coating liquid over time), which were inadequate in the prior art.
As a result of diligent study, the inventor has found that the high sensitivity and the excellent manufacturing suitability (stability of a dissolved coating liquid over time) are compatible by the following improvements of the ultra-thin tabular grain emulsion each having an equivalent circle diameter of 1.0 xcexcm or more and a thickness of 0.10 xcexcm or less: (1) introducing dislocation lines at a fringe portion of the grains; (2) when viewed from a direction perpendicular to the (111) main plane, increasing the proportion of hexagonal or triangular tabular grains whose edge and/or corner are partly hollowed; and (3) monodispersing the distribution of equivalent circle diameters of the grains.
The above object of the present invention has effectively been achieved by the silver halide emulsion and the silver halide photographic light-sensitive material using the emulsion, according to the present invention as follows.
That is,
(1) A silver halide photographic emulsion containing silver halide grains wherein a variation coefficient of distribution of equivalent circle diameters of all the silver halide grains is 40 to 3%, and tabular grains, which satisfy the following requirements (i) to (iv), account for 50% or more of the total projected area of the silver halide grains:
(i) silver bromoiodide or silver bromochloroiodide tabular grains having (111) faces as main planes,
(ii) the equivalent circle diameter is 1.0 xcexcm or more and a thickness is 0.10 xcexcm or less,
(iii) ten or more dislocation lines per grain are present at a fringe portion of the grain, and
(iv) when the grain is viewed from a direction perpendicular to the (111) main plane, it has a hexagonal or triangular shape whose edge and/or corner are partly substantially hollowed toward inside thereof;
(2) The silver halide photographic emulsion according to (1), wherein the tabular grains, which satisfy the above requirements (i) to (iv), account for 80% or more of the total projected area;
(3) The silver halide photographic emulsion according to (1) or (2), wherein the variation coefficient of distribution of equivalent circle diameters of all the silver halide grains is 25 to 3%;
(4) The silver halide photographic emulsion according to (3), wherein the variation coefficient of distribution of equivalent circle diameters of all the silver halide grains is 15 to 3%; and
(5) A silver halide photographic light-sensitive material having at least one silver halide emulsion layer on a support, wherein at least one of the silver halide emulsion layers contains the silver halide light-sensitive emulsion described in any one of (1) to (4).
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.